In order to meet high-efficiency and high-power density requirements, a resonant converter is widely applied to a Direct Current (DC)-DC power converter. However, due to the fact that a secondary-side rectification diode may cause a quite high conduction loss, a circuit composed of rectification diodes is replaced by a rectifier circuit composed of transistors, and the rectifier circuit is applied to the resonant converter. Compared with a conversion circuit adopting the rectification diodes, the circuit adopting the transistors for rectification can reduce a power loss. A conventional synchronous rectifier control method is as follows:
1, a current flowing through a secondary-side synchronous rectifier parasitic diode is detected by using a current transformer, a synchronous rectifier is turned on when it is detected that the current flows, however, due to the fact that the current transformer has parasitic inductance, a current signal and a turn-on signal are likely to delay, and the current transformer is likely to be interfered, thereby increasing the cost and the size; and
2, a control signal of the synchronous rectifier is the same as or different from that of a main power mosfet, and a driving signal of a synchronous driving tube, serving as a control signal of the synchronous rectifier, is relatively easy to obtain, but when the synchronous rectifier works in a discontinuous current mode, the control signal of the synchronous rectifier is relatively difficult to acquire, and if a signal which is the same as or different from that of the main power mosfet is directly adopted, the problems of reverse current flowing and the like will be caused so as to seriously affect the working of the circuit.